Polymers, commonly referred to as plastics, are widely used in the manufacturing of microelectronic devices. In addition to their many desirable properties, such as low cost, light weight, strength, ductility and ease of processing, polymers can be created free of metals and inorganic constituents that may interfere with sensitive clean room fabrication processes in multiple ways. For example, the loose molecular structure of polymers may allow the unwanted permeation of gases and simple liquids in fabrication facilities. This paper will provide a brief introduction to factors that influence permeation through polymers, discussing polymer structure background and its relation to permeation, and the influences of various polymer properties on permeation.